Presentation is loading. Please wait.

Presentation is loading. Please wait.

In Chan Song, Ph.D. Seoul National University Hospital

Similar presentations

Presentation on theme: "In Chan Song, Ph.D. Seoul National University Hospital"— Presentation transcript:

1 In Chan Song, Ph.D. Seoul National University Hospital
Propeller MRI In Chan Song, Ph.D. Seoul National University Hospital

2 Contents: Propeller sequence
(Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction) Motion artifact Theoretical basis Applications

3 Motion Cause  Periodic: cardiac motion, respiration, blood flow
Sporadic: irritable patients’ motion Translation, rotation, through-plane Artifact in MRI blurring and ghosting Cause Longer encoding step

4 Scan time= TR x matrix x Average  Long scan time

5 MR image reconstruction
under the assumption of object’s motion-free condition during whole k space coverage

6 Motion artifacts -Most ubiquitous and noticeable artifacts in MRI
due to voluntary and involuntary movement, and flow (blood, CSF) -Mostly occur along the phase encode direction, since adjacent lines of phase-encoded protons are separated by a TR interval that can last 3,000 msec or longer -Slight motion can cause a change in the recorded phase variation across the FOV throughout the MR acquisition sequence

7 Motion artifact: ghost and blurring

8 Solution for motion compensation
-Navigator echo usage to estimate the motion or motion related phase from extra collected data -Cardiac and respiratory gating -Respiratory ordering of the phase encoding projections based on location in respiratory cycle -Signal averaging to reduce artifacts of random motion -Short TE spin echo sequences (limited to spin density, T1-weighted scans). Long TE scans (T2 weighting) are more susceptible to motion


10 Motion (abrupt)  phase error  position error
Solution Phase information Navigation  Motion correction by phase information

11 Key ideas in propeller sequence
K space: partial covering for whole image Motion detection: blade usage Correction: FFT properties’ usage

12 Diagram of the PROPELLER collection reconstruction process for motion corrected MRI.

13 Data acquisition Propeller filling Rectangular filling kx ky

14 Phase Correct Redundant data must agree, remove phase from each blade image Imperfect gradient balancing, Eddy current effect:  echo center shift


16 James G. Pipe

17 Windowing Before After Phase correction

18 Bulk Transformation Correction
Fourier transform correspondence Image space  k space Translation  Phase roll Rotation  Rotation Separate estimation of rotation and translation

19 rotate imagerotate data
Fourier Transform Properties rotate imagerotate data

20 Rotation correction (magnitude image)
Reference (only inner circle) Magnitude of the average of strips Rotation (only inner circle) Correlation

21 Blade by blade operation
Rotation at maximum correlation  Correction

22 Fourier Transform Properties
shift image  phase roll across data b is blade image, r is reference image

23 max at Dx

24 Translation Complex average k-space data Reference (only inner circle) Complex of the average of strips Multiplication Inverse FT (maximum)

25 Blade by blade operation
Translation at maximum correlation  Correction

26 Blade Correlation throw out bad – or difficult to interpolate - data

27 Through-plane motion :low weighting coeff.

28 Reconstruction (FFT) non-Cartesian sampling requires gridding  convolution Kx Ky

29 w/motion correction

30 no correction correlation correction only motion correction only full corrections

31 Artifact reduction due to head motion
T2-FSE T2-Propeller T2-Propeller(corrected)

32 DWI-EPI B=1000s/mm2 DWI-Propeller (FSE) James G Pipe, 2002

33 DWI (b=700s/mm2) a. EPI (TR/TE/avg=2700/113/15) b. Propeller EPI (TR/TE/blade=1600/70/26) Wang FN, 2005

34 Useful application in propeller sequence
Motion- or Bo-inhomogeneities – insensitive Irritable patient Diffusion weighted image Limitations in propeller sequence Redundant acquisition  Long scan time: High SAR: problem in higher field MR system Solutions  Undersampling (Konstantinos Arfanakis, 2005) Parallel imaging Turbopropeller (James G Pipe, 2006) Propeller EPI

35 Propeller sequence Low sensitivity to image artifacts, Bo inhomogeneity and motion T2-, Diffusion-weighted images (High SNR, low geometric distortion, low SAR)

36 References 1. Pipe J, MRM 42(5): 963-62,1999.
2. Pipe J, et al., MRM 47(1): 42-53,2002 3. Wu Y, Field AS, Alexander AL. ISMRM, Toronto, Canada, 4. Roberts TP, Haider M. ISMRM, Kyoto, Japan, 5. Sussman MS, White LM, Roberts TP. ISMRM, Kyoto, Japan, 6. Pipe J and Zwart N. Magn Reson Med 55:380–385, 2006. 7. Cheryaukaa AB, et al. Magnetic Resonance Imaging 22: , 2004

Download ppt "In Chan Song, Ph.D. Seoul National University Hospital"

Similar presentations

Ads by Google